1. Technical Field
The present invention relates to a photopolymerizable composition, and a photopolymerizable inkjet ink, an ink cartridge containing the ink and a coated matter coated therewith.
2. Description of the Related Art
PCT Japanese published national phase application No. 2004-526820 discloses a photopolymerizable composition and a photopolymerizable inkjet ink using (meth)acrylic acid ester.
However, many of monomers used in conventional photopolymerizable inkjet inks have toxicities. Particularly, inexpensive and easily-obtainable (meth)acrylic acid esters occasionally cause allergies when contacting skins.
The present inventors have found some (meth)acrylic acid esters and (meth)acryl amides having no problem of skin sensitization. As disclosed in Japanese published unexamined application No. JP-2012-140593-A, they noticed that methacrylate is less toxic than acrylate and suggested an inkjet ink mainly using methacrylate.
The inkjet ink is required to have low viscosity even when including various materials such as a pigment and an additive so as not to prevent the ink from ejecting. Water can be included therein to lower the viscosity and the photopolymerizable inkjet ink including water is known. However, since penetration drying cannot be expected from non-permeable substrates as mentioned later, a process of vaporizing water is needed for higher printing speed and efficiency, resulting in enlargement of the apparatus.
When the photopolymerizable composition is used for brush coating, an organic solvent can be used. Since the organic solvent is volatilized and discharged in the atmosphere, the organic solvent is preferably used in a minimum amount in consideration of influence on the environment. On the other hand, when used as an inkjet ink, the organic solvent having high volatility occasionally increases viscosity of the ink, resulting in poor rejection thereof. The organic solvent needs adjustment in volatility for the ink to stably eject.